Matt
At 4.1 I would have woken them up to air on the safe side..
As to what level you automatically wake her is difficult to say, as it would depend on several factors mainly how much over night she falls, and whether this is based on the blood glucose falls between going to bed and her lowest ebb which would be anywhere between 2-3am, then increases slightly by the time she got up..
If you can work this out, then it will give a better guide for you..
Not sure if you do the 2.30am one every night or not, but what you can do is on different nights is do another BG at an hour apart, so tonght you do 2.30 and 3.30, then tomorrow you do 2.30 and 4.30 etc you can leave a night or two out or go the whole hog and have a sleepless night testing every hour this build a picture of what is happening to her blood sugar levels overnight...